alerts stop sending email

Hello  Xymon suddenly stop sending email alerts, the alerts generate and also notification logs show email sent but nothing come out from xymon, I have test send-mail from the server email is working able to get test email, I have restarted multiple tines but nothing fix the problem. There is no changeor update, just stops suddenly,  any one experience this ptoblem? Please share your solution. ThanksEli

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